1. Field of the Invention
The present invention relates to a vehicle generator mounted on a vehicle such as a passenger car or a truck.
2. Description of Related Art
There is known a power converter having a structure in which switching is made from diode rectification to synchronous rectification such that proportion of the synchronous rectification is increased gradually. For example, refer to Japanese Patent Application Laid-open No. 2009-130954 (patent document 1). This patent document 1 describes preventing large voltage variations by gradually decreasing a conduction period of rectifying diodes from 100%, while gradually increasing a conduction period of switching elements constituted of MOSFETs.
There is also known a vehicle electric rotating machine configured to interrupt its excitation current for a predetermined time period at the time of switching from power generation for a target power generation voltage through control of the excitation current (synchronous control mode) to power generation through energization of an inverter (phase control mode), and thereafter restore the excitation current, in order to prevent an uncontrollable state of the power generation voltage. For example, refer to Japanese Patent No. 3517405 (patent document 2).
However, the vehicle electric rotating machine disclosed in patent document 2 has a problem in that large variation occurs in its output or torque at the time of switching from the synchronous control mode to the phase control mode, because the excitation current is interrupted to stop power generation temporarily during this switching. Further, since the power generation after the switching is performed through energization of the inverter such that the period of the synchronous rectification is delayed, it is not possible to apply the technique disclosed in patent document 1 to the vehicle electric rotating machine disclosed in patent document 2 to reduce variation in its output or torque.